How you sense a smell, as pleasant or offensive, may be decided by a difference at the smallest level of DNA, one amino acid on one gene, researchers say.
There are about 400 genes coding for the receptors in our noses, and according to the 1000 Genomes Project, there are more than 900,000 variations of those genes. These receptors control the sensors that determine how we smell odors.
A given odor will activate a suite of receptors in the nose, creating a specific signal for the brain.
But the receptors don’t work the same for all of us, says Hiroaki Matsunami, associate professor of molecular genetics and microbiology at the Duke University School of Medicine. In fact, when comparing the receptors in any two people, they should be about 30 percent different.
“There are many cases when you say you like the way something smells and other people don’t. That’s very common,”
says Matsunami, who is also a member of the Neurobiology Graduate Program and the Duke Institute for Brain Sciences. But what the researchers found is that no two people smell things the same way.
“We found that individuals can be very different at the receptor levels, meaning that when we smell something, the receptors that are activated can be very different (from one person to the next) depending on your genome.”
The study didn’t look at the promoter regions of the genes, which are highly variable, or gene copy number variation, which is very high in odor receptors, so the 30 percent figure for the difference between individuals is probably conservative, Matsunami says.
Flavors, Fragrance, Food
While researchers had earlier identified the genes that encode for odor receptors, it has been a mystery how the receptors are activated. To determine what turns the receptors on, researchers cloned more than 500 receptors each from 20 people that had slight variations of only one or two amino acids and systematically exposed them to odor molecules that might excite the receptors.
[caption id="attachment_27362” align="aligncenter” width="640”] Hiroaki Matsunami led a team of scientists who systematically explored the triggers for specific odor receptors in the nose. Photo credit - Matsunami Lab, Duke University[/caption]
By exposing each receptor to a very small concentration—1, 10, or 100 micromoles—of 73 odorants, such as vanillin or guaiacol, the group was able to identify 27 receptors that had a significant response to at least one odorant.
The finding doubles the number of known odorant-activated receptors, bringing the number to 40. The research could have a big impact for the flavors, fragrance, and food industries.
“These manufacturers all want to know a rational way to produce new chemicals of interest, whether it’s a new perfume or new-flavored ingredient, and right now there’s no scientific basis for doing that,” Matsunami says.
“To do that, we need to know which receptors are being activated by certain chemicals and the consequences of those activations in terms of how we feel and smell.”
Joel D Mainland, et al. The missense of smell: functional variability in the human odorant receptor repertoire Nature Neuroscience 17, 114–120 (2014) doi:10.1038/nn.3598
Image: Adapted from Liz mc/Flickr